i want to know how to calculate electronic configuration and valency in chapter4 structure of atom

dear aishwarya 
acc to your class 9 level u need to know the K.L .M .N level configuration , 
then remember that K shell contain 2 electron max , and then all other 8 , so, u need to fill electron acc to atomic number . 
suppose atomic no of a element = 10 , then config = 2, 8 . 
and valency in case anything less than 8 , in the 2^nd , 3^rd and 4^th shell , then that will calculated as valency . 
and as u will increase your level , u will come to know the shell level config . 
regards